The Lib Dems promise to back the ’largest’ party – but do they mean votes or seats?

It’s entirely possible that Labour could end up with the most seats but a smaller share of the vote than the Tories.

So then, how do we, under the crazy first-past-the-post electoral system that we’re lumbered with, define the word ‘largest’.

I only ask, because, as Labour’s opinion poll ratings start to shrink and suddenly they start thinking that perhaps, this time, it would be best to do a bit of planning for how a coalition agreement might be hammered out, rather than trying to sort it on the fly (prompted by the publication of Andrew Adonis’s new book on the chaos that occurred last time), it suddenly seems a very relevant question.

In 2010, we in the Lib Dems were very clear that in any potential coalition negotiations, we would talk to the largest party first; and by largest we meant ‘most seats’. Andrew Stunnell (part of the Lib Dem negotiation team last time round) has now come out and said the same will hold true next time, should the same come to pass.

But is ‘most seats’ actually the right answer? Given the bias in the system, it’s entirely possible that Labour could end up with the most seats but a smaller share of the vote than the Tories. Under that scenario, how best to decide who gets first bite of the cherry – especially in a party like ours that believes passionately in a proportional voting system?

And suppose the combined UKIP-Tory vote suddenly gives them a perceived mandate; Monday’s ICM poll gave them 46 per cent of the vote, compared to a ‘progressive’ share of 45 per cent. Who has the largest mandate under that scenario? It’s a point the Tories can’t really make, as the opposite was true in 2010, but the Lib Dems could and should.

Given that Monday’s ICM poll results would leave Labour with a massive 68 seat majority despite only getting 34 per cent of the vote, it’s a moot point – how the Tories must regret the loss of the boundary changes now. But UKIP getting 18 per cent of the popular vote and 0 seats would surely call the legitimacy of any mandate into question?

Of course, you’ll say, this all presumes that the Lib Dems have any seats left to form a coalition with. But even the ICM score of 11 per cent, our lowest share with them since 1997, would still give us 35 seats on a uniform swing. If the UKIP vote starts to bleed back to the Tories, suddenly that share looks very important.

There’ll be a lot of chatter, speculation and positioning between now and the 2015 election. But come the morning of 8 May, how the leader of the Lib Dems interprets the word ‘largest’ is likely to have a profound impact on who forms the next government.

Richard Morris blogs at A View From Ham Common, which was named Best New Blog at the 2011 Lib Dem Conference